This invention relates broadly to an apparatus and method for controlling operational parameters such as the pressure, temperature and in some cases the flow rate of a fluid and, in particular, for controlling these parameters when the fluid is a polymer. More particularly, the apparatus of this invention is a novel valve assembly, optionally modified with an extension on its downstream end for collecting and compacting material emanating from the valve. The valve assembly has numerous uses and is particularly suitable for use in polymer processing equipment in which the polymer is subjected to elevated temperatures and pressures. The valve assembly of this invention provides a means for quickly and conveniently accommodating such equipment to changes in the capacity and operational parameters which become necessary from time to time. The valve assembly is also advantageous in overcoming certain operational difficulties which occasionally affect such equipment.
A variety of equipment is available for processing polymeric materials at elevated pressures and temperatures. For purposes of clarity and illustration only, the apparatus and method of this invention will be described in connection with a single piece of processing equipment in commercial use at the present time. This equipment is commonly called an "Expander-dryer" and is commercially available from ANDERSON IBEC, Strongsville, Ohio, the assignee of this application. The "Expander-dryer" is fully described in U.S. Pat. No. 3,222,797 (see in particular FIGS. 1, 6-13 and the disclosure beginning in col. 7, line 36 of the U.S. Pat. No. 3,222,797. The term "Expander-dryer" as used herein means an apparatus of the type described in the U.S. Pat. No. 3,222,797.
The Expander-dryer has numerous uses but is particularly useful for drying synthetic and natural rubber-like polymeric materials such as butyl rubber, polybutadiene, polyisoprene, and the like. In such materials, the amount of water in the finished product is a critical production specification and ordinarily must be uniformly less than 0.5% and preferably less than 0.3%. Since many polymeric rubbers originally contain substantial amounts of water, e.g., 50% or more, the material must be thoroughly dried at some stage during its processing. The polymeric materials are typically dewatered to a moisture content of 5 to 20% using known equipment such as the Expeller press apparatus also described in the U.S. Pat. No. 3,222,797 and are then dried in the Expander-dryer to a product having less than about 0.5% moisture, using a unique drying procedure.
The Expander-dryer comprises (1) a processing chamber having an inlet and exit port, (2) means, such as a compaction worm assembly mounted on a rotatable shaft, for advancing the polymeric material through the processing chamber and for gradually building up the pressure within the chamber, (3) means for gradually increasing the temperature of the polymeric material as it passes through the chamber and (4) discharge means such as a die plate disposed at one end of the chamber in order to maintain suitable back-pressures in the processing chamber. As the polymer advances through the processing chamber, the temperature and pressure are progressively increased. A unique feature of the Expander-dryer is that a sufficiently high pressure is maintained within the processing chamber to prevent the moisture associated with the polymeric material from vaporizing within the chamber at the temperatures present in the chamber. This is accomplished by preventing release of the pressure built-up within the chamber through the cooperation of the composition worm assembly and the die plate.
As wet polymeric material is discharged from the processing chamber through the die plate, it enters a zone whose pressure is sufficiently low to cause the hot liquid present in the polymeric material to rapidly flash or vaporize. Some liquid is forcibly ejected from the polymer in droplet form at this point. The polymer and residual liquid contain sufficient B.T.U.'s to flash substantially all the residual liquid to vapor in the low pressure zone. Escape of the vaporized liquid from the polymer causes an expansion of the polymer to a porous structure (hence the name "Expander-dryer") which permits the continued evaporation of the liquid until a substantially dry polymer is obtained.
The discharge die plate commonly used with such apparatus is ordinarily an apertured plate with a fixed number of apertures and a fixed aperture size. As a result, if, as is often the case, it becomes necessary to adjust the capacity or other operational parameters of the Expander-dryer beyond that for which the die configuration is suitable, the apparatus must be shut down and a suitable change made to obtain the desired die configuration. This down-time can be costly and bothersome, and could be advantageously eliminated by a discharge plate which permitted the required adjustment of capacity or other operational parameters of the apparatus while it continued in operation.
Moreover, as pressurized heated polymer is discharged from the apparatus into the zone of reduced pressure, the moisture rapidly flashes to vapor, often with a violent and explosive force. In the case of polymers, such as styrene-butadiene and polybutadiene rubbers which have relatively low tensile strengths and viscosities, there is a marked tendency for at least a portion of the polymer to fragment, disintegrate, or otherwise subdivide into very fine particles typically having a dimension of 0.5 millimeters, or less. These fragmented materials are referred to in the art as "fines."
The "fines" present several problems. For example, they must be collected using hoods and other collection equipment to prevent undue contamination of the atmosphere. In addition to the loss of polymer caused by the fines, they also have a tendency to coat the surfaces of the hoods and collection equipment where, upon standing for prolonged periods of time, they degrade. The fines coating the inside surfaces also tend to pick up moisture from the environment. Since the hoods and collection equipment are necessarily in close proximity to the dried discharged product, great care must be taken to insure that these degraded or moistened fines do not find their way back into the dried product to contaminate it with degraded or moist material. Isolated specks of wet fines in a product can result, for example, in a product whose moisture content exceeds specification. A suitable means for safely and conveniently recovering, collecting and converting the fines to a form in which they could be more easily handled would be most advantageous.
It is, therefore, a general object of this invention to provide a valve assembly and method whereby the pressure, temperature and in some cases, the flow rate of a fluid-like material such as a polymeric material, can be quickly and conveniently adjusted and regulated without the necessity for interrupting the flow of the fluid or for shutting down the equipment through which the fluid is flowing.
It is another object of this invention to provide an apparatus and method for collecting and reagglomerating into a useful form the fines produced when a polymeric material is discharged from an Expander-dryer.
It is another object of this invention to provide an apparatus and method for preventing contamination of the dried polymeric product emanating from an Expander-dryer with degraded or moistened fines.
It is a further object of this invention to provide an apparatus and method for (1) controlling the pressure and temperature and in some cases also the capacity of an Expander-dryer without taking the equipment out of operation, (2) collecting and recovering fines discharged from such an Expander-dryer before they can pick up moisture, or degrade and (3) reagglomerating these collected fines into a form in which they can be more conveniently handled and used.
It is a still further object of this invention to provide an apparatus and method for adjusting the capacity and operational parameters of various types of known polymeric processing equipment such as extruders and the like.
These and other objects of this invention will be apparent to one skilled in the art from a total consideration of this disclosure.